1. Field of the Invention
The invention relates generally to a secondary clutch and more particularly to a disconnect, or one-way bearing between the Continuously Variable Transmission (CVT) and the final rotating member to give torque release in reverse torque conditions.
2. Description of the Prior Art
U.S. Pat. No. 5,720,681 issued Feb. 24, 1998, to Benson for a Torque Responsive Actuation Device. Benson discloses a three-surfaces cam similar to the disclosure of Laughlin, Deschene, and Butterfield et al (U.S. Pat. Nos. 3,605,510, 3,605,511 and 4,216,678, respectively). Benson applies crowned, or laterally radiused, rollers similar to those shown by Steuer (U.S. Pat. No. 3,722,308) to improve driven sheave performance. Sheave faces are biased toward the initial, or minimum separation position by a torsion spring.
U.S. Pat. No. 4,969,856 issued Nov. 13, 1990, to Miyata et al for a Pulley-Type Speed-Shifting Device. Miyata et al discloses a pulley-type transmission that can be manually set at any desired ratio. The structure of the cam follows is similar to that of the disclosed driven sheave cam follower in that a spider with two rollers is used to set the separation of the sheave halves. Engine braking is provided with this transmission system by a tensioner that prevents belt disengagement during operation.
U.S. Pat. No. 4,523,917 issued Jun. 18, 1985, to Schildt for a Variable Pitch Diameter Torque Sensing Pulley Assembly. Schildt discloses a cam-actuated torque-responsive pulley that has two steps in the cam angles. When the sheave faces are between their greatest separation and mid-range (i.e., the effective diameter is small), a low cam angle (e.g., 30xc2x0) causes a high axial force to be applied to the belt. When the sheave faces are between mid-range and their closest, the axial force applied against the belt is lower because the cam angle is steeper (e.g. 45xc2x0). The cams and cam followers are symmetrical making the pulley bi-directional. An example of the use of the pulley as a drive pulley is given in which the driven pulley is fixed-pitch. The ratio of that system is varied by changing the distance between the driving and the driven shafts.
U.S. Pat. No. 4,378,221 issued Mar. 29, 1983 to Huff et al for a Torque Cam Assembly for Variable Speed Drive and Follower Element therefor. Huff et al disclose a driven sheave that can operate rotating in either direction. Also described is a cam surface-contacting plastic wear button that has a quicker break-in time than some earlier buttons.
U.S. Pat. No. 3,722,308 issued Mar. 27, 1973 to Steuer et al for a Bearing of the Conical Discs of an Infinitely Variable Cone Pulley Transmission. Steuer discloses an improved shape for the rollers that transmit power from the moveable sheave element to the driven shaft. The attempt is to overcome wear of the rollers and inclined ramps on which the sheave spacing adjustment rollers operate. It may be that the design of the disclosed driven sheave element reduces the need for the remedy disclosed by Steuer.
U.S. Pat. No. 3,605,511 issued Sep. 20, 1971 to Deschene for a Self-Cleaning Centrifugal Clutch. Deschene discloses a radially grooved shaft between the two faces of the CVT drive split sheave disclosed by Laughlin. The grooves are said to reduce belt wear when the engine is idling and the vehicle is stopped. In addition, any build-up on the shaft is cleared by operation of the drive sheave.
U.S. Pat. No. 3,365,967 issued Jan. 30, 1968 to Moogk for a Stepless Variable V-Belt Driving Gear With Asymmetric V-Belt. Moogk discloses a pair of rollers that contact cams to maintain constant speed in response to varying torque. A compression spring provides a biasing force against which the rollers and cams act.
U.S. Pat. No. 2,900,834 issued Aug. 25, 1959, to Bessette for an Automatic Variable Speed Pulley. Bessette discloses a V-belt pulley that automatically adjusts the effective diameter of the pulley in accordance with the load applied to it. A moveable split sheave face is moved toward a fixed sheave face by cams acting against radially extending pins. A torsion spring biases the sheave faces toward the initial or starting condition. Rollers in complementary inclined tracks or grooves can be used in place of the pins and cams.
U.S. Pat. No. 2,623,400 issued Dec. 30, 1952, to Davis for a Power Transmission and Centrifugal Clutch. Davis discloses a centrifugal clutch that moves split drive sheave faces toward each other to engage a V-belt. A spring-loaded driven split sheave serves as a belt-tightener.
U.S. Pat. No. 2,276,186 issued Mar. 10, 1942, to Getchell for a Pulley Construction. Getchell discloses a split-sheaved pulley that is much more complex than the design disclosed herein. Both halves of the sheave are moveable on the shaft and all power is transmissed through a spider keyed to the end of a shaft.
Current clutches have a spider or similar part, which ties the post to the moveable sheave. This spider is usually keyed or splined to the shaft on the inside diameter and has a roller or puck contacting the cam on the outside diameter. The cam in turn is typically connected to the moveable sheave. This design works very well for delivering torque from the engine through the primary clutch and belt to the secondary clutch and in turn directing power to the ground.
This system, however, becomes inefficient when there is a reversal in torque and back shifting. This torque reversal occurs when the operator releases the throttle at which point the engine RPM drops, and because of inertia, the rear tires or track continue at a greater ratio of speed compared to the engine. Back shifting refers to the amount of time that it takes the engine to regain the optimum RPM, for example 8000, once the operator goes back to wide open throttle. With current designs a very heavy spring in the secondary clutch is necessary in order to get optimum back shift into the correct ratio. (A lighter spring would give the clutch better up shifting, thus increasing torque sensitivity.) In current designs the tuner has to balance up shifting and back shifting performance.
When the operator releases the throttle, the engine RPM lowers, the belt clamping force in the primary clutch drops and the engine drops to a lower power level. If the secondary clutch can""t follow the primary and shift into a lower ratio fast enough, it will take the engine longer to run at an ideal RPM, usually around 8000 in the case of snowmobiles. Note that if the secondary clutch is in the correct ratio or the ratio is too low, the engine will reach optimal RPM more quickly than it would if the secondary clutch is in too high a ratio.
With the current designs to get optimum back shifting a very stiff spring is necessary with the result that the belt life is shortened, fuel mileage is diminished, top end speed is lowered, torque sensitivity in the cam is lowered and overall efficiency drops. If a soft spring is incorporated these problems are relieved but the CVT will not then back shift as fast as it would with the stiff spring.
In most secondary clutches of current design, the stationary sheave is typically fixed to the post. The moveable sheave rotates about and moves longitudinally on the post. As the CVT system changes ratio, the moveable sheave rotates relative to and moves toward or away from the stationary sheave. The sheaves typically have over 500 lbs of belt squeezing force during acceleration and over 100 lbs in no-torque situations. Because of this force and the rotational movement between the two sheaves there is a significant amount of friction for the secondary clutch to change ratio. This is referred to as belt smear. A heavy spring is necessary to overcome the belt smear and force the clutch to shift into a lower ratio.
In the design of the clutch with no relative motion, as shown in FIGS. 1-9 of the present application, it is not necessary to overcome the belt smear because it has been eliminated in the design. However, a heavy spring is possibly still needed to get the secondary clutch to follow the primary clutch into a lower ratio because of the reverse torque coming through the system.
The present invention addresses the problems associated with the prior art and provides for a one-way torque carrying bearing to allow for a disconnect when reverse torque is delivered.
The current design using a one-way bearing alleviates the problems of decreased efficiency, fuel mileage, belt life, and top end speed while providing good back shifting. The one-way bearing is applicable in either a tied together or non-tied together secondary clutch portion of a rubber belt CVT. Belt smear in reverse torque applications is eliminated or minimized allowing for the use of a lighter spring which in turn improves upshifting (acceleration) and torque sensitivity. The one-way bearing in the clutch system allows the secondary clutch freedom to follow the primary clutch in reverse torque conditions.
When the rider lets off the throttle, the engine will slow down causing the speed sensing primary clutch to drop its belt squeezing force. In prior art systems with the secondary connected to the final rotating member of the drive train, the secondary may not follow the primary and drop into a lower ratio and, depending on the compression spring and how much back driving torque there is, may even shift into a higher ratio. When the operator returns to wide-open throttle, the engine bogs until the CVT, primarily the secondary clutch, shifts back to a lower correct ratio. This is caused by the physical inertia of the vehicle, which in turn causes slower deceleration of the vehicle in comparison to that of the engine. This imbalance in deceleration between vehicle and engine is called back driving. In the present invention, the one-way bearing will disengage the secondary clutch from this back driving, or reverse, torque. Because the secondary clutch is disconnected from this reverse torque, it can follow the primary clutch to a lower correct ratio for acceleration at wide-open throttle.
The one-way bearing housed in the spider is the primary torque carrying member for the moveable half of the secondary clutch in a non-tied together version. It would engage when the operator is trying to put torque through the CVT. Half of the torque would go through the stationary sheave to the post. The other half of the torque would follow through the moveable sheave, through the cam into the spider, into the one-way, into the spider collar, and into the post. When there is a negative torque, the one-way bearing would disengage allowing the post and spider/cam/sheave to rotate at different RPM. That is, the post RPM will be dictated by the track or tire and the moveable sheave RPM will be dictated by the primary clutch. This can be described in the use of a snowmobile when an operator locks up the brake for an instant and then immediately turns the throttle wide open. As soon as the brake is released, the track accelerates the jackshaft and secondary clutch, either keeping the secondary element in too high of a ratio or driving the secondary element into an even higher ratio. As soon as the operator goes back to wide open throttle, the engine bogs until the CVT shifts back to the correct ratio and then the engine operates at the optimum RPM. The one-way bearing would alleviate the problem of negative torque by allowing the secondary element to follow the primary down to a lower ratio resulting in improved throttle response and efficiency.
The one-way bearing housed in the spider is the primary torque carrying member for the secondary clutch in a tied together version. It would engage when the operator is trying to put torque through the CVT. Half of the torque would go through the stationary sheave through the connecting point and into the moveable sheave. The other half of the torque would follow through the moveable sheave, then all the torque would go through the cam into the spider, into the one-way, into the spider collar, and into the post. When there is a negative torque, the one-way bearing would disengage allowing the post and spider/cam/sheave to rotate at different RPM. That is, the post RPM will be dictated by the track or tire and the secondary clutch RPM will be dictated by the primary clutch. This can be described in the use of snowmobile when an operator locks up the brake for an instant and then immediately turns the throttle wide open. As soon as the brake is released, the track accelerates the jackshaft and secondary clutch, either keeping the secondary element in too high of a ratio or driving the secondary element into an even higher ratio. As soon as the operator goes back to wide open throttle, the engine bogs until the CVT shifts back to the correct ratio and then the engine operates at the optimum RPM. The one-way bearing would alleviate the problem of negative torque by allowing the secondary element to follow the primary down to a lower ratio resulting in improved throttle response and efficiency.
The one-way bearing can incorporate a lower rate compression spring without losing the performance of the heavy spring for good back shifting and at the same time gaining the increased efficiency, fuel mileage, belt life, and top end speed typically found with a lower rate compression spring. For a standard secondary clutch, springs will start at about 120-160 pounds in the lowest ratio and increase to 280-340 pounds in high ratio. With a one-way bearing in the system the spring forces can be lowered to around 50 pounds in low ratio and 100 pounds in high ratio.
In one embodiment, the invention is a continuously variable transmission driven element for mounting on a rotatable shaft and adapted for use in a belt-type continuously variable transmission operatively connected by an endless belt to a drive element. The driven element includes a post adapted and configured to be connected to a rotatable shaft. The post is fixedly extending from a hub. A conical-faced, belt contacting sheave fixed portion extends radially from the hub. A conical-faced, belt contacting moveable sheave portion is axially and rotatably moveable on the post. A cam, having a cam surface is operatively connected to the moveable sheave portion. A spider is operatively connected to the post. The spider has a sliding member which is positioned on the cam surface, wherein rotation of the cam on the spider moves the moveable sheave portion along the post. A torque carrying one-way bearing is operatively connected to the driven element, the one-way bearing is positioned between the shaft and the spider, wherein the one-way bearing is a torque carrying member delivering torque from the engine to the rotatable shaft and decouples the driven element from the rotatable shaft during delivery of reverse torque by the rotatable shaft.
In another embodiment, the invention is an assembly having a continuously variable transmission. A final rotating member of a drive train is operatively connected to the continuously variable transmission. A torque carrying one-way bearing is operatively connected between the continuously variable transmission and the final rotating member, wherein the one-way bearing couples the continuously variable transmission and the final rotating member during delivery of torque and decouples the continuously variable transmission and the final rotating member during delivery of reverse torque.
In another embodiment, the invention is a torque sensing clutch for mounting on a rotatable shaft. The clutch includes a cylindrical base member and a first sheave operatively connected to the cylindrical base member. The first sheave is rotatable on the cylindrical base member and is stationary relative to the longitudinal movement of a cylindrical base member. A second sheave is longitudinally moveable and rotatable on the cylindrical base member. A connector operatively connects the cylindrical base member to the second sheave for rotating the second sheave and for moving the second sheave longitudinally on the cylindrical base member. A one-way bearing is operatively connected to the torque-sensing clutch. The one-way bearing is positioned between the shaft and the connector, wherein the one-way bearing couples the clutch and rotatable shaft during delivery of torque and decouples the clutch from the rotatable shaft during delivery of reverse torque by the rotatable shaft.
In another embodiment, the invention is a torque-sensing clutch for mounting on a rotatable shaft. The clutch includes a cylindrical base member and a first sheave operatively connected to the cylindrical base member. The first sheave is rotatable on the cylindrical base member and is stationary relative to the longitudinal movement of a cylindrical base member. A second sheave is longitudinally moveable and rotatable on the cylindrical base. A first connector operatively connects the first sheave to the second sheave, wherein the second sheave rotates and moves longitudinally as the first connector rotates the first with the second sheave. A second connector operatively connects the cylindrical base member to the second sheave for rotating the second sheave and for moving the second sheave longitudinally on the cylindrical base member. A one-way bearing is operatively connected to the torque sensing clutch. The one-way bearing is positioned between the shaft and the second connector, wherein the one-way bearing couples the clutch and rotatable shaft during the delivery of torque and decouples the clutch from the rotatable shaft during the delivery of reverse torque by the rotatable shaft.